1. Field of the Invention
The present invention relates to an X-ray imaging system suitable for medical and non-medical imaging, more in particular the present invention relates to an X-ray imaging system and wireless communications therefor.
2. Description of the Related Art
Currently, digital X-ray images are used for examining an internal structure of a human body or a subject. Such images are spatial distribution images of X-ray intensity passing through the subject. In the field of medical care and non-destructive inspection, a flat panel semiconductor imaging device (flat panel detector (FPD)) is used for obtaining a digital image used for examining the inside of a comparatively large object such as a human body. By using the FPD, a digital X-ray image, which is a digitized image of the X-ray intensity distribution, is obtained.
A digital image is generally characterized by an accurate and high-speed transmission of image information without damaging it. As typified by the technique of wireless local area network (LAN), which has developed rapidly during recent years, image data acquired by the FPD can be transmitted to a computer system by wireless transmission for purposes such as observation, storage, and management of the image data.
A difficult part of imaging an inside of a large object (subject) by using an X-ray beam is to set the subject between an X-ray source and the FPD. Generally, since the allowable movement range of the subject is small when the subject is large, the positions of the X-ray source and the FPD are changed so that the subject can be set between them.
Since it is necessary to set the FPD close to the subject, the FPD needs to be provided with a greater degree of flexibility when its position is changed than when it is not. For example, if a power control cable or an image transmission cable is connected to the FPD, the freedom of the FPD, when its position is changed, is reduced. Thus, an FPD using wireless connections (hereinafter referred to as a wireless FPD) is attracting attention. According to the progress in the technique of wireless LAN that aids in stable digital communication, the wireless FPD is close to practical use.
In addition to the high degree of flexibility in the selection of an imaging position, the wireless FPD is characterized by its flexibility in the determination of a utilization site. For example, even if a plurality of X-ray sources is provided in a plurality of rooms or locations, a plurality of wireless FPDs are not necessary. In other words, a single wireless FPD can be carried to the room or the location of each X-ray source and used. Accordingly, usability of the comparatively expensive wireless FPD can be improved.
FIG. 7 illustrates an example of X-ray imaging performed by two X-ray systems A and B. Each of X-ray sources 101 and 102 includes an X-ray tube and a collimator. High voltage control devices 103 and 104 are for X-ray generation. Each of X-ray interfaces 105 and 106 controls the high voltage control device to generate pulsed X-rays. Each of access points (APs) 107 and 108 is a wireless base station of a wireless LAN and is used for controlling the X-ray interface by wireless communication. In FIG. 7, imaging of a subject 110 is performed by the X-ray system B by using a wireless FPD 109.
One feature of the X-ray control is to generate an X-ray pulse in synchronization with a driving operation of the FPD. Thus, immediacy is required in the transmission of a control system. Normally, one AP for wireless FPD is uniquely determined for each X-ray system. To be more precise, immediate and stable control is realized according to the provision of the dedicated APs 107 and 108 for the X-ray systems A and B, respectively.
Whether to use the X-ray system A or B is set in advance before the wireless FPD 109 is used. Thus, the wireless FPD 109 is connected to either the AP 107 or 108 by wireless communication and not connected to both APs. Further, since the wireless FPD cannot include a plurality of wireless communication devices, image data is generally transmitted via the AP used for the X-ray control.
Japanese Patent No. 3494683 discusses a technique useful for solving the issues below.
Radio waves of wireless LAN can cover a comparatively wide range. Thus, as illustrated in FIG. 7, even if a user desires to perform imaging by the X-ray system B, actually the X-ray system A may be connected to the wireless FPD 109.
For example, even if the user sets the wireless FPD 109 in the vicinity of the X-ray system B, since it is the X-ray system A that is connected to the wireless FPD 109 by wireless connection, the user may perform the X-ray irradiation by using the X-ray system B, which is not connected to the wireless FPD 109, when the communication with the AP 107 is established. In this case, either the X-ray is not emitted from the X-ray system B or the X-ray is emitted but not in synchronization with the wireless FPD. Accordingly, normal X-ray imaging cannot be performed.
In order to prevent such an issue from occurring, for example, the user needs to change the setting of the wireless connection so that the X-ray system B can be used. However, when the user moves the FPD to a different location, the user tends to forget to change the setting of the wireless connection.
One of the resolution methods of such a case focuses on the distance between the X-ray source, which includes the X-ray tube and the collimator, and the wireless FPD. For example, since the X-ray imaging is generally performed by close-range imaging (normally 1 to 3 meters), whether the distance between the wireless FPD and the X-ray tube is within a distance defined in normal X-ray imaging can be used in the determination. In this case, by setting an AP that communicates with the wireless FPD at the X-ray tube or the collimator and limiting an allowable range of the wireless communication, the issue can be easily solved.
However, the original purpose of using a wireless device in the wireless FPD is to transmit the image data obtained by the wireless FPD. Thus, the intended purpose of the wireless device is not limited to confirming the correct wireless connection by setting an AP at the position of the X-ray tube, limiting the distance of the wireless communication, and substantially matching the distance of the wireless communication with the distance of the X-ray imaging.
The important thing is to reliably transmit the captured image data even if the wireless FPD is moved to a different location after imaging and, further, even if it is not at a location not appropriate for imaging. In other words, imaging with connection to the correct X-ray tube, which is realized by limiting the distance between the AP and the FPD for the wireless communication, is required as well as reliably transmitting the obtained image data regardless of the distance after imaging.